A forward heat engine is a device that converts thermal energy (heat) into mechanical work. A reverse heat engine is a device that utilizes a mechanical work input to transfer heat from a body at a low temperature to a body at a higher temperature. Countless varieties of both forward and reverse heat engines have been created. Examples of common forward heat engines include the internal combustion engine, gas turbine engines, steam turbine engines and Stirling engines. Examples of reverse heat engines include common air conditioners, refrigerators and heat pumps.
Still other engines have been constructed to permit operation of same as either a forward heat engine or a reverse heat engine at any given selected moment. External heat engines that follow the Stirling or Carnot cycles are good examples of such engines.
For either a reverse heat engine or for a forward heat engine, the engine could be configured to follow the highly efficient Carnot cycle. The efficiencies of both the forward and reverse Carnot cycles are equal to the maximum values possible according to the second law of thermodynamics for a heat engine operating between two given temperatures. Thus it is highly desirable to construct a practical heat engine that is capable of following the Carnot cycle.
The present invention represents an alternative to existing reverse heat engines, such as air conditioners and heat pumps that follow inefficient vapor compression cycles, and further represents an alternative to existing forward heat engines. Specifically, the present invention provides a heat engine that can be configured to operate as either a forward or a reverse heat engine, yet does not need to follow any particular thermodynamic cycle. By making strategic changes to the engine such as the locations of the heat exchangers and the shape of the cylinders, the working fluid of the engine could be cycled through a large variety of different thermodynamic processes.